LS1043A : "synchronous abort" at boot due to PCI config read

[Bjorn Helgaas]

On Wed, May 02, 2018 at 12:57:31PM +0000, Gilles Buloz wrote:
> Hi Bjorn,
> See attached patch (tested ok this morning)

This looks good.  Minor comments below.

I can fix minor things myself, but I do need a signed-off-by from you
before applying (see
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst)

Please add a changelog, too, and include the patch inline (as opposed
to as an attachment) if possible.

> --- include/linux/pci.h.orig	2018-03-26 16:51:18.050000000 +0000
> +++ include/linux/pci.h	2018-04-30 18:29:14.140000000 +0000
> @@ -193,6 +193,7 @@
>  enum pci_bus_flags {
>  	PCI_BUS_FLAGS_NO_MSI   = (__force pci_bus_flags_t) 1,
>  	PCI_BUS_FLAGS_NO_MMRBC = (__force pci_bus_flags_t) 2,
> +	PCI_BUS_FLAGS_NO_EXTCFG = (__force pci_bus_flags_t) 4,

Best if you can rebase this to v4.17-rc1.

>  };
>  
>  /* These values come from the PCI Express Spec */
> --- drivers/pci/probe.c.orig	2018-01-22 09:29:52.000000000 +0000
> +++ drivers/pci/probe.c	2018-05-02 13:44:35.530000000 +0000
> @@ -664,6 +664,23 @@
>  	}
>  }
>  
> +static bool pci_bridge_child_bus_ext_cfg_accessible(struct pci_dev *bridge)
> +{
> +	int pos;
> +	u32 status;
> +
> +	if (!pci_is_pcie(bridge) || /* PCI/PCI bridge */
> +	    (pci_pcie_type(bridge) == PCI_EXP_TYPE_PCIE_BRIDGE) || /* PCIe/PCI bridge in forward mode */
> +	    (pci_pcie_type(bridge) == PCI_EXP_TYPE_PCI_BRIDGE)) {  /* PCIe/PCI bridge in reverse mode */
> +		pos = pci_find_capability(bridge, PCI_CAP_ID_PCIX);
> +		if (pos)
> +			pci_read_config_dword(bridge, pos + PCI_X_STATUS, &status);
> +		return pos && (status & (PCI_X_STATUS_266MHZ | PCI_X_STATUS_533MHZ));
> +	}

Please arrange this so everything fits in 80 columns.

If you can split it into several simpler "if" statements rather
than one with a complicated expression, that would also be good.

> +
> +	return true;
> +}
> +
>  static struct pci_bus *pci_alloc_child_bus(struct pci_bus *parent,
>  					   struct pci_dev *bridge, int busnr)
>  {
> @@ -725,6 +742,19 @@
>  	/* Create legacy_io and legacy_mem files for this bus */
>  	pci_create_legacy_files(child);
>  
> +	/*
> +	 * if bus_flags inherited from parent bus do not already report lack of extended config
> +	 * space support, check if supported by child bus by checking its parent bridge
> +	 */

Wrap to fit in 80 columns.

> +	if (bridge && !(child->bus_flags & PCI_BUS_FLAGS_NO_EXTCFG)) {

The double negative makes this a little bit hard to read.  Maybe it
could be improved by reversing the sense of something?

> +		if (!pci_bridge_child_bus_ext_cfg_accessible(bridge)) {
> +			child->bus_flags |= PCI_BUS_FLAGS_NO_EXTCFG;
> +			dev_info(&child->dev, "extended config space not accessible due to parent bridge\n");

In v4.17-rc1, there's a pci_info() that should work here (instead of
dev_info()).

> +		}
> +	} else {
> +		dev_info(&child->dev, "extended config space not accessible due to parent bus\n");
> +	}
> +
>  	return child;
>  }
>  
> @@ -1084,6 +1114,9 @@
>  	u32 status;
>  	u16 class;
>  
> +	if (dev->bus->bus_flags & PCI_BUS_FLAGS_NO_EXTCFG)
> +		return PCI_CFG_SPACE_SIZE;
> +
>  	class = dev->class >> 8;
>  	if (class == PCI_CLASS_BRIDGE_HOST)
>  		return pci_cfg_space_size_ext(dev);